Star Trek: Voyager S1E12: Heroes and Demons

Overview

Stardate: 48693.2 Harry Kim disappears from the holodeck while role-playing in his medieval holo-novel, "Beowulf." According to the characters, he died at the hands of a mystical beast called "Grendel." When Chakotay and Tuvok investigate and also disappear, Janeway transfers the Doctor to the holodeck for his first Away Mission: to investigate/rescue the three vanished crewmembers. Kes encourages the Doctor to pick a name for himself and chooses Doctor Schweitzer. In the story, he survives fear, romance, and heartbreak to unmask the unlikely trespasser as a photonic alien life form taking the form of Grendel and turning missing crewmembers into energy.